I'll be brief: I recently built a living room gaming PC after six years away from the hobby. I did not get a discrete GPU because I wanted to wait to see what Nvidia would do with Kepler in the $150-250 range. Now I'm thinking I might just go ahead with AMD.

I'm looking at either a Radeon HD 7770 or a 7850 but my question is, can this build handle a 7850? I can do some quick math and say even with a 7850, under reasonable load, this system should not pull more than 300 watts, but I'm no expert and it's been a long time since I built a PC. I'm worried there are factors I'm failing to consider.

So I think you should be fine, if you have enough power on the 12v line.

AMD's website vastly over estimates how much you need for a variety of reasons. There are a lot of crappy PSU's that don't deliver anything close to what they're rated at (Antec doesn't make the best PSU's, but they're OK) would be the biggest one.

I usually go overkill on the PSU. I'm runnin a 700W in a system that probably only pushes 400W max. For one, it gives me the warm fuzzies, and second, it leaves plenty of room for upgrading and adding stuff later.

You'll be fine with a reasonable brand like Antec. The 172W in TR's review is power draw at the wall, so if you assume the PSU used for the test is 85% efficient, the power draw from the PSU is only around 150W. Your PSU can manage 360W (30A) on the +12V rail which accounts for most of the power usage (CPU & GPU both use 12V), so you'll have at least 100% margin.

AMD's PSU recommendations are to cover people with cheap no-name PSUs with over-inflated ratings. For example, here's a cheap 500W PSU on Newegg that actually only offers 204W (17A) on the +12V rail. The rest of the "500W" is made up with unnecessary 15A ratings on the +3.3V and +5V rails. If you had this, you really would be chancing it with a 7850 in your system.

A four-year-old, dusty Antec 380W psu, it was one of Antec's cheaper units that they gave away with cases for next to nothing (i.e. the case with the PSU was price-competetive with similar cases sans PSU)Anyway, at some point after digging it out of the parts box, it ended up powering an overclocked Core2 Quad (95W at least) and an 8800 GTX (155W spec). More than a few splitters/adapters were used by the time I was done, because the machine also had three hard drives, three 120mm fans, an SSD, a DVD drive, a seperate soundcard, wireless-G card and (as the cherry on top) a pair of XBox360 controllers.

It's probably not good to run a PSU at full load, but somewhere around half load is what you should aim for. Your 77W cpu and 130W 7850 wil probably push your system's total peak TDP up to around 275W, but peak TDP is really is rare these days. When the GPU is at full load, the CPU will likely be running cool, waiting for it to finish frames. When the CPU is running flat out, the graphics card probably isn't even running a 3D application these days. I bet you could run your 7850 system off a 250W FlexATX Pico PSU (from a decent brand at least), not that I'd recommend it, of course

Some people ask me why I have always enclosed my signature in spoiler tags; There is a good reason for that, but I can't elaborate without giving away the plot twist.

leftyassassin wrote:Thanks everyone for the insight. It sounds like a 7850 will be no problem at all.

Just out of curiosity, though... what about a 7870? A 7950? A GTX 670? Would any of those be feasible?

It míght work, but I'd strongly advise against it, your PSU has only one PCI-express power lead. You might get away with adapters off the molex connectors, but I wouldn't advise it unless your machine has almost no other hardware in it; You have only a single 12V rail in your PSU and although it's a good 30A rail, a CPU and two PCI-E connectors is a lot to ask of it - expect hot & noisy if you do run a second 6-pin PCI-e connector off it using adapters.

For reference, these are the power and socket configurations of the cards you've asked about. 7850 would be the sensible place to stop, but if you are going to risk it, a GTX 670 is probably your best bet. It can draw MORE than the 7870 in things like Furmark and OCCT but most benchmarks using game tests show it pulling 15-20W less than a 7870 from the wall.

You should be fine. I ran a Radeon HD 4870 (160W TDP) and a Core 2 Quad for extended periods in FurMark and Prime95 off an Antec Earthwatts 380W, and peak use was only 220W or 250W from the wall (something like that), well under PSU capacity.

if you are unsure just look at tr's reviews, and see what their test system (not just the vid card, the entire system) draws. get a psu (seasonic recommended; antec is over-rated) that has 2x max wattage that your system will draw at load (so if max load is 300w, get a 600w psu). the reason is that psus are most efficient at about 50% load.

Wow, I never expected my post to garner this much discussion. Thanks again for all your input.

I decided to go ahead with a 7850, the MSI Twin FrozrIII. Seems like the sweet spot for the system I've built, plus I got it for $220, which is just about what I was willing to spend. I think I probably could have gotten a GTX 670 and been fine but I don't really NEED it. I figure rather than spend $400 on a GPU now I can spend half that and, in two years, get whatever new hotness is available at the same $200 price point.

Anyway, thanks again. Now if you'll excuse me, I have a UPS man to impatiently wait for.

Hey lefty so what did you decide on? I hope the 7870, although the 7850 is also a fine choice and they both overclock great. Overclocked i think the 7850 runs just as fast as the gtx580 at less then half the voltage. The 7870 overclocked beats it at half the the voltage along with 2gb of memory over the 580s 1.5gb.

I wish i could trade my 1ghz stable EVGA 560ti Superclocked cards for a pair of 7870s...even 7850s. I cannot wait until the 7850s are 200$ and the 7870s are 250$. They are definitely overpriced even with the current price drop, they outperform the 6970 and nip at amd's own 7950 with ease but i know they cost a heck of a lot less to manufacture then the 6950 or 6970 let alone a 7950. With many more chips per wafer and less power circuitry needs then there 6000 series parents.

So far the 7850-70 series of cards are the most efficient but powerful design among AMD's 7000 series cards. But that's my opinion

vargis14 wrote:I hope the 7870, although the 7850 is also a fine choice and they both overclock great. Overclocked i think the 7850 runs just as fast as the gtx580 at less then half the voltage. The 7870 overclocked beats it at half the the voltage along with 2gb of memory over the 580s 1.5gb.

I don't imagine you'd have too much luck achieving high overclocks on an HD 7870 with a 400W PSU, especially if you start raising voltages by any real margin. But by all means, give it a try if so inclined. If you have one of those inexpensive kill A Watt, you can get a rough idea on system power draw when pushing your card at higher clocks.

Antec, like most other PSU "manufacturers" gets most if not all of its power supplies from OEMs. They have models that compete with the best of the best enthusiast power supplies, such as the HCP-1200 and new HCP-1000 Platinum, made by Delta, as well as some more mediocre PSUs they've sold over the years. I would agree with the sentiment that, in general, Antec PSUs are above average (including the OP's), but because they source them from different OEMs, you really need to take each one as they come.